The present invention relates to a position detecting mechanism, a retainer mechanism, a safety mechanism and a slider mechanism for a reading-out device in a disc player, which reading-out device enables the reading out of a signal recorded on the recording disc.
In case of an optical video disc player, a disc having a surface on which a number of pits are recorded is provided, a laser beam is projected onto the disc surface with the disc rotated at a high speed, and light reflected from the disc is optically read out and converted into an electric signal for reproduction of an image and/or sound. In such an optical video disc player, a reading device must be mechanically moved in a radial direction of the disc to follow the track of the disc. It is preferable that such movement be very smooth. For this reason, in the prior art disc players, V-shaped grooves are formed in a guide rail and a slider on which a reading-out device is fixedly mounted, roller bearings are inserted between both grooves and held by hemming parts thereof to thereby reduce kinetic friction. However, in the prior art construction, the retainer is moved only through bearings pressingly disposed between the slider and the guide rails, the bearings being movable and rotatable. If there is a slip of the bearing rotation, upon accumulation of enough slip, the retainer may deviate from the grooves of the guide rails. In order to prevent slip, it is necessary to support the bearings on both sides with a strong force of 10 kg or more. This leads to an inconvenience in use.
Moreover, it is preferable that the bearings always be in contact with the slider with a constant relationship therebetween in order to smoothly move the slider. However, in the prior art construction, there is no constant relationship between the bearings and the slider, and the bearings are not necessarily located on the gravitational center of the slider. Furthermore, the retainer is not directly held by any of the guide rail and the slider. It is, therefore difficult to accurately mount the retainer with respect to the guide rail and the slider during assembly. Also, it is necessary to hem parts of the retainer in order to prevent the roller bearings from falling out of the retainer.
In case of an optical video disc player, a reading device must be mechanically moved in a radial direction of the disc and follow the track of the disc. In general, the movement of the reading device is from the inside to the outside of the disc. In case that the disc is always rotated at a constant rotational speed (a CAV type), since the tracking error is more remarkable in the inner circumference of the disc than in the outer circumference thereof, when a reading device (pick-up) is located at a predetermined position, it is necessary to vary the gain of a tracking servo loop system to thereby decrease the gain at the inner circumference portion of the disc in comparison with the gain used at the outer circumference portion of the disc.
The sensitivity to tangential error is greater on the inside portion of the disc than on the outside portion thereof. Therefore, when the pick-up reaches a predetermined position, the gain of the tangential servo system is varied to thereby decrease the servo system gain at the inner circumference with respect to that in the outer circumference portion. On the other hand, in case that the tangential speed of the disc is maintained constant (a CLV type), to maintain a constant time error a greater compensation is needed in the inside portion of the disc than in the outside portion thereof. Accordingly, when the pick-up reaches the predetermined position, the gains of the spindle servo system must be changed to thereby increase the gain in the inner portion of the disc.
For these reasons, a detecting mechanism for detecting the direction of movement of the reading device in the radial direction of the disc is needed for the video disc player. Furthermore, a plurality of positions thereof must be detected. Thus, there is a need for a detecting mechanism for detecting the relative positions between the reading device and the disc with a high accuracy.